as PDF - Scientific Research Publishing

Natural Resources, 2014, 5, 1007-1019
Published Online December 2014 in SciRes. http://www.scirp.org/journal/nr
http://dx.doi.org/10.4236/nr.2014.516085
Facing the 2013 Gold Rush: A Population
Viability Analysis for the Endangered
White-Lipped Peccary (Tayassu pecari)
in Corcovado National Park, Costa Rica
Christian J. Rivera
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, USA
Email: [email protected]
Received 25 September 2014; revised 6 November 2014; accepted 23 November 2014
Copyright © 2014 by author and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
Abstract
The white-lipped peccary (Tayassu pecari) is facing range-wide declines throughout the Neotropics. It has been eliminated from about 89% of its historical range in Costa Rica. Corcovado National
Park, in the Osa Peninsula of Costa Rica, is the last remaining stronghold for the white-lipped peccary in the country. In 2013, the Park experienced a sudden gold rush that brought with it a wave
of 250 miners and vigorous hunting pressures on the population. Given that the species is endangered and is susceptible to hunting due to its herding behavior and tendency to cohere and attack
when threatened rather than flee, it is important to assess its probability of extinction under various hunting scenarios. Incorporating data from studies on the life history of the species throughout its range in the Neotropics and in Corcovado, I used the population viability analysis software
VORTEX to simulate the population trajectories and probabilities of extinction of the species under current hunting pressures and under various management scenarios. The results of this study
revealed that under the 2013 scenario where 250 miners were present in the Park, the population
of white-lipped peccaries has a about a 40% chance of extinction within five years and about a 99%
chance of extinction within 10 years. Moreover, there is an “extinction threshold” for the population between the presence of 100 and 150 miners hunting in the Park. At this threshold, the population growth rate, r, drops from a positive growth rate (r = 0.09, SD = 0.08) to a negative one (r =
−0.07, SD = 0.29). I suggest that anti-mining and anti-poaching laws be enforced immediately, and
that the number of miners be reduced to 100 at a minimum, if not completely, in order to ensure
that the population of white-lipped peccaries becomes viable and evades a local extinction.
Keywords
Corcovado National Park, Population Growth Rate, Population Viability Analysis, White-Lipped
Peccary
How to cite this paper: Rivera, C.J. (2014) Facing the 2013 Gold Rush: A Population Viability Analysis for the Endangered
White-Lipped Peccary (Tayassu pecari) in Corcovado National Park, Costa Rica. Natural Resources, 5, 1007-1019.
http://dx.doi.org/10.4236/nr.2014.516085
C. J. Rivera
1. Introduction
1.1. Corcovado National Park
Home to a range of biological richness that has attracted scientists and tourists to the region for decades [1]
Corcovado National Park (CNP) can be found in southwest Costa Rica in the Osa Peninsula. This region is part
of the Mesoamerican biodiversity hotspot as defined by Myers et al. [2]. The protected area is about 470 km2
and is composed of a range of the following habitats: lowland rainforest, highland cloud forest, jolillo palm forest, mangrove swamps, marine coasts, and beach habitats. The Park receives around 5000 mm of rainfall annually, with the wettest months September and October and the driest months January to April [3] [4]. All six of
Costa Rica’s feline species as well as all four of its monkey species can be found in CNP. There are more than
6000 species of insects, 117 reptile and amphibian species, over 500 species of trees, more than 360 species of
birds, and 140 species of mammals [1].
1.2. The White-Lipped Peccary (Tayassu pecari)
Amongst others, the Park is home to the endangered white-lipped peccary (Tayassu pecari), which has been
eliminated from about 89% of its historical territory in Costa Rica and is now facing range-wide declines in
Central and South America [5]. The conservation status of the white-lipped peccary in the IUCN Red List of
Endangered Species has recently been changed from “near threatened” to “vulnerable” because of rapid population declines attributed to habitat loss, disease epidemics, competition with livestock, and illegal hunting [6].
Early studies by Kiltie [7] suggested that white-lipped peccaries serve as key ecosystem engineers by foraging
around trees, roots, and shoots on the forest floor and significantly reducing the densities of certain fruits that
grew near these objects. Foraging and herding behavior of the peccaries also results in wallows and puddles that
collect water and serve as habitats for aquatic species [8]. Furthermore, they have been found to enhance the
germination rates under parent palm trees and affect plant survival, recruitment, and spatial distribution; this is
done by trampling, eating, and dispersing palm seeds [9]-[13].
In his early studies, Leopold [14] noted that white-lipped peccaries were amongst the first big mammals to
become locally extinct when humans fragmented tropical forest habitats in Mexico and Central America. This is
due to the synergistic effects of habitat loss and overhunting. Long-lived mammals such as the white-lipped
peccary show greater declines in abundance than do short-lived mammals, thus making them more vulnerable to
population declines and extirpation [15]. The lower productivity of white-lipped peccaries also makes the species more susceptible to hunting, compared to the collared peccary [16]. Herds form very strong cohesive units
where individuals are rarely seen alone [17] [18]. Furthermore, individuals of this species prefer to confront
threats and cohere when attacked, increasing their vulnerability to hunting when facing armed humans [19]-[21].
1.3. Conflicts and Conservation
Since its establishment, CNP has been the site of a conflict between conservation and the exploitation of its
natural resources, notably logging, wildlife trading, poaching, and gold mining. Fortunately, ecotourism has
helped create jobs so that locals can deviate from subsistence farming and hunting, logging, and mining. Despite
these efforts, critical conservation issues still exist [22] [23].
In 2005, 30 - 40 illegal gold miners were reported to be active in CNP [23]. The numbers continued to increase and by 2013, 250 illegal gold miners had established themselves in CNP, building tunnels for mining
gold and hunting the fauna of the Park for subsistence during the gold extraction operations. Law enforcement
has not been able to impose severe restrictions on criminal activities, with those who are arrested for mining being released within a few days and facing minor penalties. The high levels of poverty in the region, due to failed
reforestation projects and the departure of banana-producing companies, are accounting for the gold rush [24][26]. Moreover, the tunnels that are built disturb the landscape and vegetation of the Park and the extraction
process, which involves mercury, contaminates the rivers and creeks [23].
On April 2013, the Ministry of the Environment sent an alert to the country in regards to the decline of jaguars (Panthera onca) in the Osa Peninsula [27]. Vice Minister of the Environment, Ana Lorena Guevera, declared that the decline of jaguars is attributed to the decline of the white-lipped peccary, which is the main food
source for the jaguar and has been heavily hunted inside and outside the protected areas of the Peninsula as the
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number of gold miners has increased [27]. Furthermore, a 20-year study on the relative abundance of the
white-lipped peccary and the jaguar has shown a declining trend [28]. Gold miners working illegally in CNP
organize themselves in groups of 20 - 30 individuals and spend up to three weeks in the Park, hunting most animals they come across but relying on about two white-lipped peccaries per group to sustain them during that
time [29] [CNP ranger, pers. comm.]. Other estimates of hunting inside CNP are lacking.
Before the 2013 gold rush, the areas that presented the most opportunistic hunting of white-lipped peccaries
were the areas outside the Park borders [30] [31]. The conflict between the white-lipped peccaries and the people living in the surrounding towns and villages also exists because the animals eat the crops as they expand
their foraging range during the end of the wet season in September [32]. Today, it is widely accepted that the
only known threat driving the decline of the white-lipped peccary population is the intensive levels of poaching
that occur within the Park, since the area is large enough to maintain a viable population of at least 500 individuals [27] [33] [34] [CNP ranger, pers. comm.] [E. Carrillo, pers. comm.] [J. C. Sáenz, pers. comm.].
In this study, my objective is to perform a population viability analysis (PVA) to model the population trajectories of white-lipped peccaries in CNP under various hunting pressure scenarios. PVAs are quantitative tools
that use demographic and habitat data of a species to estimate probabilities of extinction or decline as well as
chances of recovery given identifiable threats [35] [36]. I integrate published data on the life history of the species with known hunting levels as well as possible hunting scenarios. The scenarios include various numbers of
illegal gold miners hunting in the Park. I will suggest the most appropriate conservation and management strategy to maintain a viable population of white-lipped peccaries in Corcovado National Park.
2. Methods
2.1. Simulation of the Population
I modeled the white-lipped peccary population using the population viability analysis software VORTEX (version 9.999). The software models deterministic forces and provides a “stochastic simulation of the extinction
process” of wildlife populations. The iterations simulate the life cycles of sexually reproducing, diploid organisms based on life history parameters that are inputted by the user and various default values provided by
VORTEX [37]. VORTEX models sequential events that describe an annual cycle of the species and individual
organisms based on the inputted parameters and random probabilities. The results of the simulations provide a
quantification of threats to extinction of the populations being modeled [36]. The efforts of Fuller et al. [38]
have attempted to quantify the annual mortality rates of the white-lipped peccary population in CNP. The authors reported the survival and cause-specific mortality rates of adult male and female white-lipped peccaries
over a period of six years. Using the mortality rates from this study, I ran a baseline simulation (Scenario 1) that
excludes any mortality from poaching and thus models the population under no hunting pressure.
I set the initial population size for all simulations at 250 individuals. This was the average population size estimated to be present in the Park in 1999 [39] as well as in the beginning of 2013 [40]. I ran the simulations
1000 times for a period of 50 years in order to inform management strategies for the near future.
2.2. Baseline Simulation of the White-Lipped Peccary Population (Scenario 1)
A baseline scenario that models the trajectory of the white-lipped peccary population under no hunting pressure
is needed to compare and assess population viability at various hunting levels. Table 1 lists the variables and
values I obtained from the published literature to create the baseline simulation of the white-lipped peccary
population. The following variables were obtained from studies performed directly on the white-lipped peccary
population in Corcovado National Park: number of populations, reproductive system, female mortality, male
mortality, initial population size, and carrying capacity. The baseline simulation (Scenario 1) models the population with mortality rates taken from Fuller et al. [38], which presents survival and death rates of the whitelipped peccaries in Corcovado. The mortality rates are calculated as the sum of the mortalities from the following causes of death: poaching, predation, accident, and unknown. For the purpose of this scenario, I did not take
into account poaching mortality.
Because life history data on this species is limited, estimates had to be made for the following variables: percent of males in breeding pool, age distribution of initial population, and SD in carrying capacity (see Table 1).
In their studies on the reproduction of white-lipped peccaries in CNP, Altrichter et al. [41] concluded that the
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Table 1. Life history and other parameters of the VORTEX model used to simulate the baseline scenario of the white-lipped
peccary population in Corcovado National Park.
Variablea
Explanation/Notes
Value chosen
Reference
# of iterations
# of times simulation is run
1000
# of years
# of years the population is modeled
50
Extinction definition
How extinction is defined in the model
1 sex remains
# of populations
# of populations to be modeled
1
[40]
The level and effect of inbreeding depression
3.14 lethal equivalents;
50% due to alleles
[45]
Reproductive system
The mating system
Polygynous
[41]
Age of first reproduction in F
Age at which F begin breeding
2
[44]
Age of first reproduction in M
Age at which M begin breeding
2
[44]
Maximum age of reproduction
Age of F/M when breeding ends
13
[44]
Maximum # of progeny
produced/year
Maximum # of offspring produced/F/year
3
[16]
Sex ratio at birth
Sex ratio of offspring at birth
1:1
[16] [41]
Density dependence in
reproduction
Relationship between reproduction and
population density
No relationship assumed
% of adult F breeding
Proportion of F breeding each year
62%
[42]
EV in % breeding
Environmental variation in % of
adult F breeding each year
3.74
[16]
Distribution of # of
offspring/F/year
Statistical distribution characterizing
the # of offspring produced each year
Normal Distribution
Scenario Settings
Species Description
Inbreeding depression
Reproductive System
Reproductive Rates
Mean # of offspring/F
2
SD in # of offspring/F
0.5
[16]
Mortality Rates
F mortality
Mortality of F as % and SD
18%, SD = 5.09
[38]
M mortality
Mortality of M as % and SD
3%, SD = 2.60
[38]
No variation in
survival across ages
[43]
Mortality for age categories
Mate Monopolization
% males in breeding pool
% of adult M breeding each year
77%
Age distribution of initial
population
Distribution of individuals by age
at the beginning of the simulation
Stable age distribution
Initial population size
Number of individuals at the
beginning of the simulation
250
[39] [40] [J. C.
Sáenz, pers. comm.]
Carrying capacity (K)
Carrying capacity of the environment
1000
[3]
SD in K
SD in carrying capacity of the environment
200
Initial Population Size
Carrying Capacity
a
# = number, F = female, M = male, EV = environmental variability, SD = standard deviation.
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mating system of the species is a polygynous one. In such mating systems, a higher percentage of males than
females breed in the population as a result of strong male-male competition over females. Bodmer [42] found
that the proportion of females breeding per year in this species was 62%. Because no life history data on the
percent of male white-lipped peccaries that breed each year exists, and because it is known that the peccaries in
CNP are dominated by a polygynous system, I assumed that about 15% more males than females are in the
breeding pool.
There are also no data on the mortality rates for age categories of white-lipped peccaries, thus the variable
mortality for age categories was taken from a study on an intensively hunted wild boar population (Sus scrofa)
and assumes that there is no variation in survival across ages in the population [43]. The authors suggested that
their results on the mortality rates of wild boar are comparable to rates of typical ungulates.
If the habitat carrying capacity changes over time due to variation in the environment (as is the case for the
dry and wet season in CNP), it is suggested that a standard deviation for carrying capacity (K) be included in
VORTEX, and that this standard deviation be less than K/3 in order to reduce the chance that K drops to zero
during the simulation [36]. Altrichter and Almeida [30] observed that the white-lipped peccaries might move
beyond the boundaries of CNP to other forested regions of the Osa Peninsula (central and southeastern) at the
end of the wet season (September-December). This suggests that seasonal changes may drive the size of the
population because they can expand their range, thus it is important to account for a fluctuation in K. Because
standard deviation in carrying capacity is entered as a number of animals in VORTEX, I assumed an estimated
standard deviation of 200 individuals for a carrying capacity of 1000 individuals [3], which is less than K/3 (K/3
≈ 333).
2.3. Simulation of Known Hunting Pressures (Scenarios 2 - 3, 8) and Consideration of
Alternative Management Strategies (Scenarios 4 - 7)
In order to model the known mortality rates of the white-lipped peccary population in CNP in 2002 (Scenario 2),
I adjusted the baseline scenario (Scenario 1) to account for mortality from poaching and simulated the population under the known hunting pressure reported by Fuller et al. [38] for males and females. All scenarios (see
Table 2) use the parameters from the baseline model and the number of males and females hunted were input
values under the “Harvest” section in VORTEX.
People residing near CNP hunt the peccaries opportunistically, mainly during a 4-month period (SeptemberDecember) when the herds are seen passing by the edge of the Park and near the six villages closest to CNP [30].
The extraction of gold also appears to occur in the dry season [46], and gold miners are known to hunt peccaries
for subsistence while in the Park. All simulations assume that hunting occurs only during this 4-month period at
the end of the wet season when the white-lipped peccary population increases its seasonal range to search for
food and is more susceptible to detection by hunters [47] [48]. Because Scenario 2 incorporates mortality values
from the literature (which accounts for mortality from poaching), hunting pressure is defined by these values and
not by calculated levels of harvesting in VORTEX.
It has been observed that the peccaries are hunted as soon as they reach the Park borders and as they travel
past villages [30]. Under current conditions, the miners poach the white-lipped peccaries that attempt to expand
their range outside the Park. This makes it even difficult for tourists and Park personnel to spot the herds. Similarly, locals living around the Park do not have the same access to the peccary herds and are no longer the primary group of people hunting the animals [CNP ranger, pers. comm.]. Thus, the subsequent scenarios (Scenarios 3 - 8) assume that hunting pressure is based only on hunting by the number of illegal gold miners reported in
the Park. The simulations for Scenarios 3 - 8 assume that each group of miners contains between 20 - 40 individuals [23], and that each group hunts two white-lipped peccaries per hunting month [CNP ranger, pers.
comm.]. There appears to be differential exposure to hunting based on the observation that males travel in the
back of the herd while females and young travel in the front of the herd and frequently escape [41]. Of the peccaries hunted, I assumed that 70% of them were males while 30% were females.
In 2006, it was reported that an estimated 30 illegal gold miners resided in CNP [46] compared to the 250
miners calculated to reside in the Park during the 2013 gold rush [24]. Table 2 summarizes the hunting scenarios based on the number of illegal miners in 2006 (Scenario 3) and 2013 (Scenario 8), as well as the peccaries
hunted under alternative management scenarios where the number of miners in CNP increases in increments of
50 until reaching 2013 levels.
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Table 2. The table summarizes the scenarios simulated based on mortality rates without hunting pressure, mortality rates
(with poaching) reported in Corcovado National Park in 2002, the number of miners reported during 2006 and 2013, and
alternative scenarios where the number of miners increases in increments of 50 until reaching 2013 levels. Hunting is
assumed to occur only by the miners during the end of the wet season when gold extracion activities occur and when the
peccaries expand their foraging range (September-December). The number of males and females hunted were input values
under the “Harvest” section in VORTEX.
Scenario
Description
Scenario
starting
year
Miners
in CNP
Total number of
individuals hunted
per end of wet season
Males
hunted
Females
hunted
1
Baseline scenario based on 2002
mortalities for males and females in
CNP. No mortality from poaching.
2002
0
0
0
0
2
Mortality rates for males and females in
2002. Includes pressure from poaching.
2002
0
0
0
0
3
Poaching rate based on number of
miners in CNP during 2006.
2006
30
16
11
5
4
Alternative scenario.
2014
50
16
11
5
5
Alternative scenario.
2014
100
32
22
10
6
Alternative scenario.
2014
150
48
33
15
7
Alternative scenario.
2014
200
64
44
20
8
Poaching rate based on number
of miners in CNP during 2013.
2013
250
80
56
24
3. Results
3.1. Running the Simulations
I ran 1000 simulations of the white-lipped peccary population for each of the eight scenarios. I recorded the
mean final population size, the mean probability of extinction for the population after 50 years, the mean time to
first extinction (if any simulations went extinct), and the mean growth rate r of the population (see Table 3). The
mean growth rate, r, is calculated prior to truncation due to the carrying capacity of the environment. Truncation
refers to the addition of mortalities on the population to keep at it the upper limit, K.
3.2. Growth Rates and Probabilities of Extinction
As expected, the highest growth rate is that of the baseline scenario (Scenario 1; r = 0.15, SD = 0.05) where
hunting is not incorporated into the simulations. Even with 100 miners hunting (Scenario 5), the population
shows a mean positive growth rate (r = 0.09, SD = 0.08). Negative growth rates are reported when there are
more than 150 miners in the Park (Scenarios 6 - 8).
Under the baseline scenario, the population of white-lipped peccaries had a 0% chance of going extinct, as it
did in Scenario 2 (2002 hunting level), Scenario 3 (30 miners), and Scenario 4 (50 miners). There appears to be
no difference between Scenarios 3 and 4. The probability of extinction for the population increases drastically
between Scenario 5 (100 miners) and Scenario 6 (150 miners; about a 74% increase in probability of extinction).
If 250 miners continue to hunt (Scenario 8), the population will be extinct after 50 years, with the mean time to
first extinction occurring in about five years.
Figure 1 plots the mean number of extant individuals for Scenarios 1 - 3 and 8. The population trajectories
for the baseline scenario and Scenarios 2 and 3 steadily increase while Scenario 8, which models the population
with 250 miners in the Park during 2013, models a population that goes extinct. Figure 2 shows the mean number of extant white-lipped peccaries under various management scenarios where the number of miners in the
Park increases in increments of 50 until reaching 2013 levels. The graph shows that under Scenario 7 (200 miners) and Scenario 8 (250 miners) the population goes extinct.
3.3. Probabilities of Extinction under Various Management Scenarios
The probabilities of extinction for various management scenarios are reported in Figure 3. Year 1 for Scenario 8
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Table 3. The table shows the mean population size of the 1000 simulated white-lipped peccary populations (which includes
both extant and extinct simulations) as well as the probability of extinction of the population after 50 years. The mean time to
first extinction applies only to the population simulations that went extinct in the scenario. The mean growth rate r was
calculated prior to truncation by the carrying capacity K.
Scenario
Miners (n)
Mean final population
size (95% C.I.)
Mean probability of extinction (%)
After 50 years
Time to first extinction:
mean years (SD)
Mean growth
rate r (SD)
1
0
908 (898 - 917)
0
0
0.15 (0.05)
2
0
861 (852 - 869)
0
0
0.10 (0.05)
3
30
901 (891 - 910)
0
0
0.13 (0.05)
4
50
905 (895 - 914)
0
0
0.13 (0.05)
5
100
824 (807 - 840)
7.2
20.7 (7.6)
0.09 (0.08)
6
150
163 (141 - 184)
81
13.8 (5.8)
−0.07 (0.29)
7
200
1 (0 - 2)
100
7.8 (1.9)
−0.37 (0.44)
8
250
0
100
5.6 (0.7)
−0.50 (0.44)
Figure 1. The figure shows the mean number of extant individuals after 1000 simulations
for Scenarios 1 - 3 and Scenario 8. The starting population for each scenario was 250
white-lipped peccaries. For Scenarios 2, 3, and 8, year 0 represents the years 2002, 2006,
and 2013, respectively. The figure includes standard error bars.
corresponds to the year 2013, thus year 5 is 2018 and year 10 is 2023. Scenarios 4 and 5 present promising probabilities of persistence for the peccaries where the probability of extinction for the population approaches zero
when there are only 50 miners poaching and is only about 7% after 50 years with 100 miners in the Park. This is
reflected in Figure 2 where the population trajectories for both scenarios show a steady increase until they reach
the carrying capacity (K = 1000, SD = 200).
The population under Scenario 6 reaches more than a 60% chance of extinction by year 15 and the probability
continues to increase as a function of time. Under Scenarios 7 and 8, the population is at more than a 95%
chance of extinction by year 10.
4. Discussion
4.1. Growth Rates and Probabilities of Extinction
Growth rates are valuable indicators of the viability of a population. Bodmer et al. [15] examined the likelihood
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Figure 2. The figure shows the mean number of extant individuals after 1000 simulations
for Scenarios 4 - 8. The starting population for each scenario was 250 white-lipped peccaries. For Scenario 8, year 0 represents year 2013. For all other scenarios in the figure, year 0
represents year 2014. The figure includes standard error bars.
Figure 3. The figure shows the probabilities of extinction under the 2013 scenario where
250 miners were reported in Corcovado National Park (Scenario 8) as well as various
management scenarios where the number of miners varies by increments of 50 people.
For Scenario 8, year 0 represents year 2013. For all other scenarios in the figure, year 0
represents 2014. Note the change in probabilities of extinction between Scenario 5 and
Scenario 6 after 50 miners have been added.
of extinction in Amazonian mammals and calculated estimates of the species’ intrinsic rate of natural increase,
rmax. For the white-lipped peccary population in the Northeastern Peruvian Amazon, the authors reported a rmax
of 0.84. In my PVA, the highest mean growth rate for the population in CNP resulted from the baseline scenario
where no poaching was accounted for in the mortality rates of males and females (r = 0.15, SD = 0.5). This
suggests that mortality rates of the white-lipped peccary population in 2002 were very high in CNP compared to
those in the Peruvian Amazon in 1997. It is important to note that some of the cause-specific mortality rates reported by Fuller et al. [38] have wide confidence intervals (i.e. mortality rate for females from unknown causes,
but not poaching = 0.12, 95% C.I. = 0.04 - 0.20), which may be a possible explanation for the difference in r
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reported by Bodmer et al. [15] and the one calculated in my baseline scenario.
My simulations confirm Fuller et al.’s [38] contention that the population in 2002 may have been maintaining
itself. In 2006, it was reported that about 30 people were mining in the Park. There appears to be no difference
in the mean final population sizes for the scenarios with 30 miners and 50 miners because I assumed that the
number of male and female peccaries hunted for sustenance was about the same in both cases. Nevertheless, had
the reported hunting levels from 2002 which use mortality rates that include poaching mortality from Fuller et al.
[38] and those from 2006 (30 miners) had been maintained (or had they increased to 50 miners poaching), the
population of white-lipped peccaries would have virtually no chance of going extinct even after 50 years.
The white-lipped peccary population shows positive values for r even with 100 miners in the Park, though the
scenario does report iterations that go extinct. For the iterations that go extinct, the mean time to first extinction
is about 20.7 years (SD = 7.6). For this scenario the population has a mean probability of extinction of about 7.2%
after 50 years. It appears that the white-lipped peccary population may be viable even with up to 100 miners in
CNP.
Under the 2013 hunting pressure (Scenario 8), there is a 99% of extinction within ten years, with the mean
time to first extinction occurring in about six years (by 2019) if the number of miners is not controlled immediately. The threshold that turns r into a negative value appears to occur when 150 or more miners are poaching.
This is reflected in the calculations of probabilities of extinction (Figure 3) where the population reaches about
a 23% probability of extinction at year 10 and about a 61% probability of extinction at year 15 with 150 miners.
These results indicate that it would require Park enforcement to reduce the number of miners to 100 to maintain
a viable population that has very low probabilities of going extinct. A reduction of miners from 250 to 150
would not suffice since the mean time to first extinction is about 14 years (year 2028) under the scenario with
150 miners.
Fragoso [49] attributed the local disappearance of a white-lipped peccary population in Maraca Island Ecological Reserve, Brazil, to mortality from overhunting and eventual reproductive failure. My model assumes that
more males than females are harvested per end of wet season. The selective harvesting of males and females in
the population of each scenario may be a possible explanation for the high increase in probability of extinction
that occurs when the number of miners increases from 100 to 150. Studies on the effects of selective harvesting
of male and female ungulates have reported a wide range of mechanisms by which populations may be negatively affected [50]. Adult males are more susceptible to hunting than females because of their behavior of traveling in the back of the herd [41] and because hunters tend to show preference towards adults with a large body
size [50]. Selective harvesting of males tends to shift the population sex ratio towards females and may reduce
the mean age of males in the population, which may in turn reduce recruitment and result in low population
growth rates [50]. Furthermore, male-biased harvests can reduce female fecundity (number of young born) and
lead to population declines [51].
Another possible explanation for the extinction threshold may be the harvesting intensity on female whitelipped peccaries. Because a polygynous system prevails, and because more males will continue to mate with
females regardless of the female population size, the reduction in number of females may be the limiting factor
in the growth of the population [50]. In my model, the threshold occurs when the number of females hunted increases from 10 (100 miners) to 15 (150 miners). During the same poaching conditions, the number of males
hunted increases from 32 (100 miners) to 48 (150 miners). This is alarming, as the threshold requires only about
five more females and 16 more males to be poached during the 4-month period in order to increase the probability of extinction of the population by about 74% from one scenario to the next. It appears that low-density ungulate populations with low reproductive rates may show high adult mortality because of a greater number of older
individuals [52]. This may be a possible case in the model, where not enough young, reproducing females are
present in the population at one time due to strong hunting pressure. Furthermore, elasticity analyses have
showed that the population growth rate of female ungulates may be heavily impacted when the mortalities of
sexually reproducing females are increased [53] [54].
4.2. Improvement of the Model
Due to the lack of current demographic information on the white-lipped peccary population in CNP and the assumptions that were made, it is important to highlight the improvements that can be made to the model. The
VORTEX simulations would benefit from more current mortality rates as well as current estimates of causespecific mortality rates, notably poaching. The male and female mortality rates for the population in CNP are
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C. J. Rivera
from 12 years ago and were calculated based on the monitoring of 25 females and 11 males [38]. Although
Fuller et al.’s [38] study took place over six years, a more thorough study would track a greater number of male
and female peccaries to reduce the sizes of the confidence intervals for cause-specific mortality rates. As noted
above, there is a threshold between 100 and 150 poachers mining. No variation in survival across ages is assumed [42] because studies on the survival rates of white-lipped peccaries are lacking. More thorough and recent records of mortality rates that account for variation in survival across ages may shift the threshold as well as
the probabilities of extinction for the various scenarios. There may be variation in survival across age classes
given that it is more likely for miners to hunt adult peccaries rather than juveniles if they are being poached to
feed a large group of people.
4.3. Management Recommendations
From 1990-1994, it was found that the level of law enforcement in CNP was directly linked to the abundance of
animals in the Park [55]. The species more negatively affected by the lack of law enforcement were those that
were poached for consumption, such as the white-lipped peccary. CNP had a stricter law enforcement program
compared to that of the nearby Golfo Dulce Forest Reserve, which accounted for a greater abundance of animals
in Corcovado than in the Forest Reserve. I suggest that the CNP administration invest in stricter law enforcement programs, in contracting scientists and staffs to gather accurate estimates of current mortality rates for
male and female white-lipped peccaries, and in obtaining accurate estimates of monthly hunting rates. Because
my simulations suggest that the population may go extinct in less than ten years under the 2013 hunting scenario
and because management resources may be limited, these resources should first be invested in removing around
150 miners. Full removal of the miners would be ideal, but a viable population may be maintained if 100 miners
are left in CNP.
Enforcing anti-mining and anti-poaching laws that protect the white-lipped peccary population would prevent
a negative cascade of events for CNP. It is possible that reducing white-lipped peccary numbers could lead to an
ecological extinction, reducing its function as an ecosystem-architect, seed predator, seed disperser [5] [55], and
major prey for the endangered jaguar population [28] [34]. A further reduction in white-lipped peccary abundance may induce the switching of jaguars from one prey species to another [56] [57], which could have unprecedented ecological ramifications. Because miners also hunt other species for sustenance while in the Park,
law enforcement may help reduce possible risks of population declines for species that may be susceptible to
declines due to poaching and for which there is a lack of biological information. Furthermore, stricter law enforcement will impede further transformation of the landscape and mercury contamination of the water that results from mining operations. A local extinction may be prevented through habitat protection and improved
management of hunting [58]. In this case, complete prohibition of hunting may be required especially due to the
assumptions and uncertainties surrounding the modeling of the population trajectories.
5. Conclusion
It is likely that the population of white-lipped peccaries in Corcovado National Park will go extinct in the near
future if immediate management efforts are not implemented. CNP has been known to be one of the most well
protected areas under Costa Rica’s National Park System [55]. In order to maintain this reputation, there is an
urgent need for stricter law enforcement to reduce the number of miners poaching inside the Park. Strong law
enforcement programs that limit the unsustainable harvest of endangered species will ensure that CNP remains
the largest stronghold for the white-lipped peccary in Costa Rica.
Acknowledgements
C. J. R. thanks E. Carrillo, J. C. Sáenz, and R. Salom-Pérez, and the staff at the Corcovado National Park Administrative Headquarters for providing information, data, and reports on the white-lipped peccary population
and for helping to define the scope of this study, as well as two anonymous Park rangers at La Leona Ranger
Station in Corcovado National Park. The author also gratefully acknowledges D. S. Wilcove and M. W. Tingley
for their guidance and insightful advice throughout the course of the study. This study was made possible by the
financial support and generosity of the Program in Latin American Studies and the Department of Ecology and
Evolutionary Biology at Princeton University.
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C. J. Rivera
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